There are four significant factors which affect the native product drying process:
- the vacuum within the drying tunnel,
- the product layer height on the belt,
- the belt speed and
- the temperature profile.
Of these, the effectiveness of the vacuum is especially important: Dependent upon the product and water content, the drying pressure is adjusted to between 5 and 0.5 mbar, so that free water crystallizes into ice. This ensures a gentle cooling and drying which preserves the aroma. The resulting product is a powder which is easy to re-dissolve.
Thickness Makes the Difference When it Comes to Drying
The thickness of the product layer on the belt is adjusted through a combination of the injection rate and the belt speed. A thin layer helps to provide shorter drying times and ensure economical drying. The holding time of the product within the dryer can also be determined by the belt speed. It is adjusted between 15 and 60 minutes, depending on the product characteristics, desorption behaviour, sublimation rate and maximum product temperature. During the drying process the product temperature is observed via infrared cameras.
How to Control the Temperature of Heat Sensitive Products
The product temperature is controlled via contact heating from the bottom and radiation from above. The combination of treatment methods creates a constantly dried product and prevents any damage caused by overheating. The SPX belt drying technology is further able to control the generation of color and roasted aroma from the Maillard reaction as well as enables adjustment of product bulk density. When the drying process is complete or a product change is required, the plant is automatically cleaned to maintain the highest hygiene standards.
Overall, the SPX belt dryer offers a gentle and reliable solution to produce consistent, high quality end products. The control of the vacuum and heating elements along with speed and depth of the product mean it can handle even the most challenging of drying applications to deliver required product characteristics and assured results.
* The author is Division Manager at SPX, e&e Series, e&e Process & Product Development, Warendorf, Germany.